1. Field of the Invention
The present invention relates to an apparatus for writing Bragg gratings, and more particularly, to an apparatus for writing Bragg gratings and a reflection unit used in the apparatus capable of readily adjusting an incident angle of light radiated from a light source, in order to write the Bragg gratings on an optical fiber, a planar waveguide, a polymer waveguide, or the like.
2. Description of the Related Art
Generally, an optical fiber grating for writing Bragg gratings on an optical fiber is an optical fiber device for periodically or non-periodically varying an index of refraction of an inner core of the optical fiber to reflect a certain wavelength of light or to generate transmission loss. The optical fiber grating is employed in various devices used in the field of optical communications, such as an optical add/drop multiplexer (OADM), a wavelength add/drop multiplexer (WADM), a dispersion compensator, a wavelength selection reflection mirror, a wavelength removing filter, a specific wavelength transmission filter, an optical laser, a mode converter, and a gain flattering filter of an erbium-added optical fiber amplifier.
A conventional apparatus for writing Bragg gratings will now be described. FIG. 1 is a view of a conventional apparatus for writing Bragg gratings.
Referring to FIG. 1, the conventional apparatus 100 for writing Bragg gratings includes a light source 101 for radiating light, a beam splitter 103 for converting a path of the light radiated from the light source 101, and first and second reflection mirrors 105 and 107 for reflecting the light whose path has been converted by the beam splitter 103 into an optical fiber 109.
The light radiated from the light source 101 is divided into a reference light beam 104a passing through the beam splitter 103, and a target light beam 104b reflected by the beam splitter 103. The target light beam 104b is reflected again toward the optical fiber 109 by the second reflection mirror 107, and the reference light beam 104a is reflected again toward the optical fiber 109 by the first reflection mirror 105.
Interference fringes are formed on the optical fiber 109 by the reference light beam 104a and the target light beam 104b reflected by the first and second reflection mirrors 105 and 107. In this process, a bright interference fringe-forming region increases an index of refraction since the light is absorbed through an optical fiber core, and a dark interference fringe-forming region does not alter the index of refraction since the light is not well absorbed.
Using this theory, Bragg gratings, in which the index of refraction of the optical fiber core periodically varies, are written. Meanwhile, in order to change the position of a target object such as the optical fiber 109 in which the Bragg gratings are written, or to adjust an interval between the gratings, an incident angle of light introduced into the target object 109 should be adjusted. For this purpose, the conventional apparatus 100 for writing Bragg gratings rotates the first and second reflection mirrors 105 and 107 to adjust a reflection angle of the light.
However, in order to adjust the reflection angle of the light, the first and second reflection mirrors 105 and 107 should be rotated according to the calculated result of the incident angle of the light beams 104a and 104b incident on the first and second reflection mirrors 105 and 107 and the reflection angle of the light reflected by the first and second reflection mirrors 105 and 107.
Therefore, whenever the position of the target object, such as the optical fiber 109, into which the Bragg gratings are written, changes, or the interval between the gratings is adjusted, it is difficult to readily adjust the incident angle of the light on the target object 109 since the first and second reflection mirrors 105 and 107 should be rotated by calculating the incident angle and the reflection angle of the light beams 104a and 104b. 